Heretofore, in the disc apparatus which records data on the disc-shaped recording medium or reproduces recorded data, there are two methods: a method for rotationally controlling the recording medium by CLV (constant linear velocity); and a method for rotationally controlling the recording medium by CAV (constant angular velocity).
CAV control method is easier to control velocity as compared with CLV control method. Further, since being able to record and reproduce control data such as track address at regular intervals, CAV control method has the advantage that track search can be executed easily. However, in CAV control method, the recording density is decreasing as recording and/or reproducing of data goes to the outer circumference, so that the total amount of recording information is deteriorated as a whole.
As a method for solving the problem, there has been proposed a zoning recording method. In the zoning recording method, data recording area of a disc is divided into a plurality of zones from the inner circumference side to the outer circumference side, and the data is recorded/reproduced with same clock frequency in track of each zone, and with changed clock frequency in track of different zone. More specifically, the clock frequency is increased as it goes from the inner circumference zone to the outer circumference zone in order to stand in proportion to the distance from the center of the disc to that zone. Therefore, it is possible to equalize the recording density of the inner circumference and the outer circumference.
This prevents from decreasing the amount of recording information at the outer circumference which has been a drawback of the CAV control.
As recording format of a disc-shaped recording medium, there are a continuous servo method and a sample servo method. In the sample servo method, the recording area is divided into servo area and data area, and reference clock and tracking error signal and the like which are standard of recording/reproducing are extracted based on the information recorded in the servo area. Actually, the servo area is formed at the center of the track, and is composed of pit for extracting clock information, and wobbling pit for extracting tracking error signal which is formed Off setting the fixed distance from the track center toward the inner circumference and the outer circumference. These pits are previously formed when the disc is made (prepit).
Heretofore, a disc-shaped recording medium using the zoning recording method and the sample servo method described above in combination is proposed (hereinafter, referred to as "zone CAV"). In aforementioned recording medium, the servo area is formed radially, and also address data area is formed radially.
Therefore, in the disc apparatus which records and reproduces the data, the reference clock is extracted from the servo area in and from this type of recording medium, thus the data can be recorded and/or reproduced based on extracted clock information in each zone under the condition of constant angular velocity. Further, address data area formed radially is detected, so that position of recording and/or reproducing can be found and further the address can be easily read while seeking.
In zoning applying a continuous servo method, ID (identification information) is invariably recorded at the top of sector in every zone. Therefore, in the disc apparatus which records and reproduces data on and from this type of recording medium, by detecting the interval from an ID to another ID, the unit sector can be easily detected.
On the contrary, in the disc apparatus which records and reproduces the data by the zone CAV applying aforementioned sample servo method, the interval from a servo area to another servo area is allotted as one segment, which is the segment including, for example, address data and the user data, or the segment of only the user data, or the segment of only address data. Therefore, the number of recordable byte of the user data is different from each segment and each zone. Consequently, sector which is the minimum unit of recording/reproducing can not be a fixed cycle, and there occurs a problem that the detection of the sector becomes difficult.
As one of the methods to solve this problem, the disc apparatus can be considered, which counts up the byte counter in every segment, and Generates sector pulse when the number of byte corresponding to one sector is obtained, thus detects sector. However, even in this manner, since there is shift of timing between at recording and at reproducing, the sector pulse is also shifted at recording and at reproducing. Therefore, a synchronizing circuit with very complicated construction is required.